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| Next: <a href="Adding-symbols-from-an-object-file.html#Adding-symbols-from-an-object-file" accesskey="n" rel="next">Adding symbols from an object file</a>, Previous: <a href="Adding-Symbols-to-the-Hash-Table.html#Adding-Symbols-to-the-Hash-Table" accesskey="p" rel="prev">Adding Symbols to the Hash Table</a>, Up: <a href="Adding-Symbols-to-the-Hash-Table.html#Adding-Symbols-to-the-Hash-Table" accesskey="u" rel="up">Adding Symbols to the Hash Table</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Differing-file-formats-1"></a> |
| <h4 class="subsubsection">2.17.2.1 Differing file formats</h4> |
| <p>Normally all the files involved in a link will be of the same |
| format, but it is also possible to link together different |
| format object files, and the back end must support that. The |
| <code>_bfd_link_add_symbols</code> entry point is called via the target |
| vector of the file to be added. This has an important |
| consequence: the function may not assume that the hash table |
| is the type created by the corresponding |
| <code>_bfd_link_hash_table_create</code> vector. All the |
| <code>_bfd_link_add_symbols</code> function can assume about the hash |
| table is that it is derived from <code>struct |
| bfd_link_hash_table</code>. |
| </p> |
| <p>Sometimes the <code>_bfd_link_add_symbols</code> function must store |
| some information in the hash table entry to be used by the |
| <code>_bfd_final_link</code> function. In such a case the output bfd |
| xvec must be checked to make sure that the hash table was |
| created by an object file of the same format. |
| </p> |
| <p>The <code>_bfd_final_link</code> routine must be prepared to handle a |
| hash entry without any extra information added by the |
| <code>_bfd_link_add_symbols</code> function. A hash entry without |
| extra information will also occur when the linker script |
| directs the linker to create a symbol. Note that, regardless |
| of how a hash table entry is added, all the fields will be |
| initialized to some sort of null value by the hash table entry |
| initialization function. |
| </p> |
| <p>See <code>ecoff_link_add_externals</code> for an example of how to |
| check the output bfd before saving information (in this |
| case, the ECOFF external symbol debugging information) in a |
| hash table entry. |
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